To your first asked question, about whether the conquest of Ireland can be seen as a form of colonialism, yes, absolutely. To your second, much more sophisticated question regarding the adoption of folklore and discipline as a form of colonialism, I would argue yes on discipline, but probably not on folklore.

I am going to punt on the history of English-Irish relations from the “conquest” of Henry II until the sixteenth century for two reasons. First, I come from the position that we can only really start talking about “colonialism” in the modern sense of the word with the discovery of the New World and the ensuing discourses and practices of empire-building that arose from that. Second, in the specific context of Ireland, it is probably simpler to start talking about colonization until the Tudors try (and fail) to subjugate Ireland There is bound to be plenty of insight to be gained from the medieval side of things (particularly as it relates to the role of the Earls of Desmond!), and any medieval Britainists should absolutely chime in and fill in that gap.

In 1534, Henry VIII defeats the Earl of Kildare and, after a failed policy of extraction led by Thomas Cromwell, in 1541, declares himself the King of Ireland as well as England. This decision put an onus on the Tudors from then on to try and make something of their Irish possessions, which their antecedents had never been truly successful at. Henry VIII followed a policy of “surrender and regrant,” where he would replace the titles of Irish nobles with English ones under the assumption that they would obey his authority. They did not. Henry, and his son Edward, however, were more interested in consolidating their authority in England and were involved in the Reformation, so Irish policy was placed on the backburner.

Under Mary I, the first attempts at colonizing Ireland began with what she called “plantations.” These were settlements of English citizens in specific points of Ireland in order to inculcate the Irish with “English” qualities, specifically in Offaly and Laoise counties. The plantation model was possibly created based on formulations by Niccolo Machiavelli. In the Prince, chapter 3, Machiavelli states that princes would be best served by sending delegations of his own people to displace and settle newly conquered lands. This would be cheaper, and it would allow the prince to focus his attention to his own immediate surroundings. While it is unknown if Mary herself read Machiavelli, many of her court probably would have been aware of him (Machiavellianism had spread like wildfire in the sixteenth century). These plantations however failed to take root, as the investment made by the Crown was not enough to sustain a population of foreigners in a hostile land. Like her father, Mary herself was also distracted by the Habsburg-Valois Wars, which threatened Tudor lands in France.

This story repeats itself for the most part with Elizabeth I. Elizabeth tried settlements with various degrees of success in the Ards Peninsula, and after the suppression of the 1583 Desmond Rebellion. In this second case, the Irish question had ironically enough become entangled with continental matters. The English Reformation had not been successfully enforced in Ireland, so Protestantism had failed to take root. Irish Catholics often rebuffed their Anglican overlords, and with the intermittent conflicts between England and Catholic Spain in the 1580s and 1590s, Elizabeth saw it fit to try to force at least some portions to heel. The Munster Plantation, taken from lands owned by the Earls of Desmond, was the largest attempt to-date to subjugate the Irish within its bounds. The situation on the ground, however, was always chaotic, as undertakers like Edmund Spenser and royal authorities like Richard Beacon (both more well known for their literary outputs) tell us. However, even Munster ended up being destroyed with the onset of the Nine Years’ War in Ireland, a large-scale rebellion that saw the Earls of Tyrone and Tyrconnell try to petition the King of Spain to launch another Armada. The Nine Years’ War did not end until James I came to the throne. He and his attorneys signed a peace agreement with the Irish Earls, and then quickly lost interest. James was more interested in settling the New World, as colonies there were more likely to be profitable.

This period (early 1600s) is generally when historians will claim that English colonialism takes off. James may have been more interested in America than Ireland, however, in 1607, the Earls of Tyrone and Tyrconnell fled to the continent, afraid that James would harshly punish them for their rebellion. With their lands now ostensibly in the King’s possession, his privy council advised him to try again with the plantation system, arguing that he was now in control of more land than any other sovereign in Europe. This marks the beginning of the Ulster Plantation, the boundaries of which more or less mark the current boundaries of “Northern Ireland,” which is still part of the UK today.

The Ulster Plantation has played a remarkable part in shaping the historical memory of Irish colonization to the present day. James was far more invested in making Ulster work, and over the course of the next 40 years (the English Civil War caused some disruptions) somewhere between 80,000 and 125,000 British settlers had settled in Ulster. New plantation owners, either Protestant or covertly Catholic, owned upwards of forty percent of the land. And of course, the indigenous Irish had been largely displaced.

The reason why I said “probably not” to your question about folklore and mythology is that, given how the theories of plantation were formulated by Machiavelli, the goal would have been to displace not only people, but culture as well. To the extent that this initial settlement can be seen as “English” over taking “Gaelic” culture, or Protestantism over Catholicism, is still under dispute. But the scale of the investment and the totality of the conversion by the 1900s at least demonstrates that English colonization of Ireland was perhaps more successful in the long run than English colonization of the New World (at least as it pertains to the monarch of England having imperial control over a territory).

So I think there is a very strong argument that yes, Irish colonization is absolutely part of the larger scheme of English imperialism from the sixteenth to the twentieth centuries. If nothing else, Howard Mumford Jones demonstrated in an older article that many of the same individuals who were undertakers in Ulster also became involved in settling Jamestown.

There are a lot of sources on this that get political. Some of the more academic ones include:

James Bardon’s History of Ulster, Nicolas Canny’s Making Ireland British, Padraig Lenihan’s Consolidating Conquest, Colm Lennon’s Sixteenth Century Ireland: The Incomplete Conquest.

The Jones article I briefly mentioned was in the Proceedings of the American Philosophical Society, called “Origins of the Colonial Idea in America,” if you have access to that.

Edit: Formatting sources a bit more clearly